The present invention generally relates to impedance matching type electrical connectors, and more particularly to an impedance matching type electrical connector applicable to the connection of a mother board and a CPU (central processing unit) board which is mounted with a CPU in computer systems.
In computer systems, a plurality of CPU boards are provided as options. A desired CPU board is connected to a mother board via an electrical connector, so that it is possible to freely improve the functions and the like of the computer system.
The electrical connector must have an impedance characteristic which matches an impedance characteristic of the mother board, so that unwanted signal reflection or the like will not occur at the electrical connector. Generally, the impedance of the mother board is 50.OMEGA..
When realizing the required impedance matching, it is most desirable to use a coaxial connector. However, a microstrip line structure or a strip line structure, having a provisionally coaxial structure, becomes more appropriate for use in the electrical connector from the point of view of the required space and cost as the number of pins or electrodes becomes large. But when the electrical connector having the microstrip line structure is used to realize the impedance matching between the mother board and the CPU board, there are problems in that the impedance becomes unstable and the crosstalk becomes high. Accordingly, it is preferable to employ the strip line structure to realize the impedance matching.
On the other hand, the number of pins of the electrical connector is approximately 300 and tends to increase with the increasing kinds of signals to be processed in the computer system.
Furthermore, there are demands to minimize the size of the electrical connector, so as to minimize the mounting space on the mother board occupied by the electrical connector. In addition, there are also demands to minimize the cost of the electrical connector.
Next, a description will be given of an impedance matching type electrical connector proposed in a U.S. patent application Ser. No. 882,005 filed May 13, 1992, which issued as U.S. Pat. No. 5,195,899 on Mar. 23, 1993 and has the same assignee as the present application, by referring to FIGS.1 through 5.
FIG. 1 shows a cross sectional view of an electrical connector 10, FIG. 2 shows an enlarged perspective view of a plug connector member 11 with a part thereof omitted, and FIG. 3 shows an enlarged perspective view of a jack connector member 12 with a part thereof omitted. FIG. 4 is a diagram for explaining the impedance matching of the electrical connector 10, and FIG. 5 shows a conceivable structure based on the basic structure of the electrical connector 10.
As shown in FIG. 1, the electrical connector 10 includes the plug connector member 11 and the jack connector member 12 which is engaged by the plug connector member 11. The jack connector member 12 is fixed on a mother board 18, while the plug connector member 11 is fixed on a CPU board 19.
As also shown in FIGS.2 and 4, the plug connector member 11 includes a main body 13 made of a synthetic resin, a first male signal terminal group 14 fixed to the main body 13 and forming a first column, a second male signal terminal group 15 fixed to the main body 13 and forming a second column, a male ground terminal plate 16 fixed to the main body 13 and positioned between the first and second male signal terminal groups 14 and 15, and a grounding shell 17 made of a metal and surrounding the main body 13.
On the other hand, as also shown in FIGS.3 and 4, the jack connector member 12 includes a main body 20 made of a synthetic resin, a first female signal terminal group 21 assembled in the main body 20 and forming a first column, a female ground terminal group 22 assembled in the main body 20, and a second female signal terminal group 23 assembled in the main body 20 and forming a second column.
As shown in FIG. 1, the grounding shell 17 of the plug connector member 11 engages the periphery of the main body 20 when the plug connector member 11 electrically connects to the jack connector member 12. More particularly, the first male signal terminal group 14 engages the first female signal terminal group 21, the second male signal terminal group 15 engages the second female signal terminal group 23, and the male ground terminal plate 16 engages the female ground terminal group 22.
As shown in FIG. 4, the first male signal terminal group 14 and the first female signal terminal group 21, the male ground terminal plate 16 (the female ground terminal group 22), and one sidewall 17a of the grounding shell 17 form a strip line structure.
Similarly, the second male signal terminal group 15 and the second female signal terminal group 23, the male ground terminal plate 16 (the female ground terminal group 22), and a sidewall 17b on the opposite side of the grounding shell 17 form a strip line structure.
Accordingly, the impedance of the electrical connector 10 is 50.OMEGA., and an impedance matching is made between the mother board 18 and the CPU board 19.
But if the number of pins were to be increased by simply increasing the number of terminals extending in the two columns, the electrical connector would become extremely thin and long, and the mechanical strength of the electrical connector would become poor.
Accordingly, it is conceivable to increase the number of pins based on the basic structure of the electrical connector 10, as shown in FIG. 5. In FIG. 5, a male ground terminal plate (female ground terminal group) is arranged between two adjacent columns of terminals, and the number of columns of male signal terminal groups is increased to four columns.
In other words, in FIG. 5, the male ground terminal plate 16 is arranged between the first male signal terminal group 14 and the second male signal terminal group 15, a male ground terminal plate 16-1 is arranged between the second male signal terminal group 15 and a third male signal terminal group 30, and a male ground terminal plate 16-2 is arranged between the third male signal terminal group 30 and a fourth male signal terminal group 31.
But according to the conceivable structure shown in FIG. 5, a pitch P.sub.1 between the two adjacent columns of terminals becomes large, that is, approximately 2.6 mm, for example. As a result, a width W.sub.1 of the plug connector member 11 becomes considerably larger than expected, and it is impossible to reduce the size of the electrical connector. In addition, because the grounding shell 17 is made of a metal, the cost of the electrical connector becomes high due to the large plug connector member 11.